There are a number of known routes for the delivery of drugs into the human or animal body. Notable among these are intravenous injections and oral delivery systems, for example tablets, capsules or orally taken liquids.
Intravenous injections have the advantage that the drug can be delivered directly into the blood stream. This means that the efficiency of this method is very high and there is little if any wastage of the drug. The amount of drug that must be delivered in a particular dose therefore is small compared to other methods of drug delivery. Non-intravenous injections are also a relatively efficient method of drug delivery.
The major disadvantage of injections, intravenous or otherwise, however, is that they are highly inconvenient, especially for example when repeated drug doses must be given to treat chronic conditions. A patient must either return to a medical professional for the injection, or must learn to give injections themselves. Patients suffering from diabetes mellitus for example must learn to give themselves regular daily injections. Apart from the inconvenience and discomfort this causes, there is also the risk of infection if the needle is not clean.
Oral delivery systems, eg tablets and capsules, are far more convenient but not all drugs can be given orally. Some drugs may not be properly absorbed through the stomach wall, others may irritate the stomach causing an unwanted side effect. Other drugs may be degraded by the gastronintestinal tract. For example, protein-based drugs, such as insulin for the treatment of diabetes, cannot be given orally since they would be degraded by proteolytic enzymes and must be given by injection.
Pulmonary drug delivery, for example through nasal sprays or tracheal instillation, offers an alternative mode of delivery to intravenous and oral systems. For example, vasopressin, an anti-diuretic protein used in the treatment of diabetes insipidus, can be given in the form of a nasal spray.
The disadvantage of pulmonary drug delivery, however, is that it is very wasteful and a relatively large amount of the drug is necessary to ensure that the correct dose is received by the patient. U.S. Pat. No. 5,006,343 to Benson et al discloses a method for the pulmonary delivery of pharmaceutically active substances in which liposomes containing pharmaceutically active substances are mixed with an amount of alveolar surfactant protein. A surfactant is a surface active agent that acts to reduce the interfacial tension between water and other liquids or solids, detergents or emulsifiers are typical examples of surfactants. A known natural surfactant is a detergent-like surfactant produced by the lung. This surfactant comprises 90% phospolipids and 10% protein, the major lipid component being dipalmitoylphosphatidylcholine (DPPC). It is an object of the present invention to provide a further development over the teachings of U.S. Pat. No. 5,006,343 and to provide a method of improving the efficiency of pulmonary drug systems whereby they may become more attractive as an alternative to intravenous injection.